Sql 带条件的BigQuery LAST_值

下面是示例数据，我希望填充expectedOutput列中的值。我想根据规则计算它——如果isValid=1，给我上次isValid=1时的结果值。因此在本例中，第1行为null，因为这是第一个值。第6行显示苹果，因为这一行是有效的，苹果是上次有有效值时的水果

row           fruit       isValid     expectedOutput (Prior valid value)
1             apple       1           NULL
2             apple       0           NULL
3             apple       0           NULL
4             apple       0           NULL
5             orange      0           NULL
6             orange      1           apple
7             grape       1           orange
8             grape       0           NULL

这是我尝试过的，并没有得到正确的结果

LAST_VALUE(case when isValid = 1 then fruit end IGNORE NULLS) OVER(PARTITION BY all ORDER BY row)

见下面的例子

#standardSQL
with `project.dataset.table` as (
  select 1 row , 'apple' fruit, 1 isValid union all
  select 2, 'apple', 0 union all
  select 3, 'apple', 0 union all
  select 4, 'apple', 0 union all
  select 5, 'orange', 0 union all
  select 6, 'orange', 1 union all
  select 7, 'grape', 1 union all
  select 8, 'grape', 0 
)
select *, 
  if(isValid = 1, lag(fruit) over(partition by isValid order by row), null) as Prior_valid_value
from `project.dataset.table` 
# order by row           

有输出

参见下面的示例

#standardSQL
with `project.dataset.table` as (
  select 1 row , 'apple' fruit, 1 isValid union all
  select 2, 'apple', 0 union all
  select 3, 'apple', 0 union all
  select 4, 'apple', 0 union all
  select 5, 'orange', 0 union all
  select 6, 'orange', 1 union all
  select 7, 'grape', 1 union all
  select 8, 'grape', 0 
)
select *, 
  if(isValid = 1, lag(fruit) over(partition by isValid order by row), null) as Prior_valid_value
from `project.dataset.table` 
# order by row           

有输出

---

您需要向窗口添加边界以排除当前行：

无界前置和1前置之间的行

试试这个：

WITH
  table1 AS (
        SELECT 1 as row,  'apple'  as fruit,  1 as  isValid  union all
        SELECT 2 as row,  'apple'  as fruit,  0 as  isValid  union all
        SELECT 3 as row,  'apple'  as fruit,  0 as  isValid  union all
        SELECT 4 as row,  'apple'  as fruit,  0 as  isValid  union all
        SELECT 5 as row,  'orange' as fruit,  0 as  isValid  union all 
        SELECT 6 as row,  'orange' as fruit,  1 as  isValid  union all 
        SELECT 7 as row,  'grape'  as fruit,  1 as  isValid  union all   
        SELECT 8 as row,  'grape'  as fruit,  0 as  isValid
)

SELECT
  *,
  CASE
    WHEN isValid = 1 THEN LAST_VALUE(IF(isValid=1, fruit, NULL) IGNORE NULLS) OVER(ORDER BY row ROWS BETWEEN UNBOUNDED PRECEDING AND 1 PRECEDING)
  END AS expectedOutput
FROM
  table1

---

您需要向窗口添加边界以排除当前行：

无界前置和1前置之间的行

试试这个：

WITH
  table1 AS (
        SELECT 1 as row,  'apple'  as fruit,  1 as  isValid  union all
        SELECT 2 as row,  'apple'  as fruit,  0 as  isValid  union all
        SELECT 3 as row,  'apple'  as fruit,  0 as  isValid  union all
        SELECT 4 as row,  'apple'  as fruit,  0 as  isValid  union all
        SELECT 5 as row,  'orange' as fruit,  0 as  isValid  union all 
        SELECT 6 as row,  'orange' as fruit,  1 as  isValid  union all 
        SELECT 7 as row,  'grape'  as fruit,  1 as  isValid  union all   
        SELECT 8 as row,  'grape'  as fruit,  0 as  isValid
)

SELECT
  *,
  CASE
    WHEN isValid = 1 THEN LAST_VALUE(IF(isValid=1, fruit, NULL) IGNORE NULLS) OVER(ORDER BY row ROWS BETWEEN UNBOUNDED PRECEDING AND 1 PRECEDING)
  END AS expectedOutput
FROM
  table1